WESTFIELD - A criminal investigation is underway in connection with the accidental shooting death of an 8-year-old boy during a firearms expo Sunday, Hampden District Attorney William M. Bennett said Tuesday.

Bennett said the probe will determine if it was legal, as well as reckless, for a child to possess or fire a machine gun.

State and city police, as well as federal investigators from the Bureau of Alcohol, Tobacco and Firearms, are involved in the investigation.

"At this point in the investigation I have found no lawful authority which allows an 8-year-old to possess or fire a machine gun," Bennett said. "Two, was it a reckless or wanton act to allow an 8-year-old to use a fully loaded automatic weapon?"

Christopher Bizilj, of Ashford, Conn., was firing a 9 mm Micro UZI machine gun at the Westfield Sportsman's Club around 2 p.m. Sunday when he lost control of the automatic combat-type weapon and shot himself once in the head. He died at Baystate Medical Center in Springfield.

An autopsy conducted Monday confirmed the boy died of a single gunshot wound to the side of the head, Bennett said.

Bennett said the investigation centers on the statute which governs firearms in Massachusetts, known as Chapter 140.

"No one can possess a machine gun without authority under Chapter 140," Bennett said, adding he has found no lawful authority under Chapter 140, or any other law, which allows an 8-year-old possession of a machine gun, or to be able to fire a machine gun.

State and local detectives have secured a video which may be relevant to the shooting, Bennett said.

They have also interviewed a number of witnesses, and are in the process of securing records and licenses relating to the event, Bennett said.

The boy's father, Charles Bizilj, who was at the event, said he gave his son permission to fire the UZI, according to the Boston Globe.

Bizilj, a physician and medical director of the emergency department at Johnson Memorial Hospital in Stafford Springs, Conn., was about to take a photo of his son when the accident occurred.

Christopher was attending the event with his brother Colin, a sixth-grader. Bizilj said it was the first time Christopher had fired an automatic weapon.

The club has held an annual firearms expo since 2002 in cooperation with COP Firearms & Training of Amherst. That company is owned by Pelham Police Chief Edward B. Fleury. Fleury has not been available for comment

The company operates machine gun shoots and provides firearms training and sales, as well as gunsmithing and other services.